1. Field of the Invention
The present invention relates to a suspension control apparatus.
2. Related Background Art
An example of a conventional suspension control apparatus is disclosed in Japanese Patent Laid-open No. 5-330325 (1993). Such a suspension control apparatus comprises a shock absorber of variable damping coefficient type disposed between sprung mass and unsprung mass of a vehicle, an actuator for setting and adjusting a damping coefficient of the shock absorber of variable damping coefficient type, an acceleration sensor for detecting an upward acceleration and a downward acceleration of the vehicle, an integration means for integrating a signal from the acceleration sensor to obtain an upward absolute velocity or a downward absolute velocity, a control target value calculating means for multiplying the upward or downward absolute velocity value by a control gain to obtain a control target value, and a control signal generating means for previously storing information representative of a relative relation (which is obtained on the basis of a feature of the shock absorber of variable damping coefficient type) between the control target value and a control signal and for generating a corresponding control signal by inputting the control target value from the control target value calculating means, whereby the damping coefficient corresponding to the upward or downward absolute velocity can be obtained to improve the comfort and steering ability of the vehicle.
By the way, theoretically, in order to suppress upward and downward vibrations of a vehicle, although it is desirable to adjust damping forces of the vehicle on the basis of the upward and downward absolute velocities of the vehicle, since a shock absorber cannot adjust the damping force directly (the damping force is a function of a piston speed multiplied by the damping coefficient), in effect, the damping coefficients are adjusted on the basis of the upward and downward absolute velocities, as is in the afore-mentioned conventional example.
Accordingly, in the afore-mentioned conventional example, the control gain/dead band is set by supposing an average or mean piston speed generated when the vehicle is running on a normal paved road surface (in this case, the vibration of the vehicle and the amplitude thereof are relatively small), and the vibration control is effected on the basis of the set value.
However, when the vehicle is running on a rough road surface (in this case, the vibration of the vehicle and the amplitude thereof are great), the actual piston speed becomes considerably greater than the average piston speed, with the result that a damping force greater than a desired damping force is generated, thereby worsening the comfort of the vehicle.